1. Field of the Invention
The present invention relates to a network communication apparatus used in TCP/IP communication.
2. Description of the Related Art
In TCP/IP (Transmission Control Protocol/Internet Protocol) communication, flow control is carried out for preventing a buffer overflow in which a reception-side node cannot process all pieces of data from a transmission-side node and a buffer becomes full. For example, in best-effort burst communication such as FTP (File Transfer Protocol) communication, an inter-node transmission rate is largely affected by a transmission channel status or a CPU load status of an apparatus. For this reason, a buffer overflow occurs relatively easily, and flow control is thus essential. On the other hand, in streaming, by controlling a band used so as to guarantee a transmission rate necessary for reproduction, a buffer overflow is suppressed as compared to the best-effort communication.
Next, flow control of the related art will be described. In a MAC (Media Access Control) layer corresponding to a lower-level sublayer of a data link layer in an OSI reference model of a network, a flow control mechanism defined by IEEE802.3x is prepared. In this flow control mechanism, a stop packet is transmitted to a transmission source to thus stop a data transmission when a remaining capacity of a reception buffer becomes small, and a stop release packet is transmitted to thus resume the data transmission upon increase in the remaining capacity of the reception buffer. Accordingly, the buffer overflow is suppressed, and a high-throughput data transmission becomes possible.
Moreover, in TCP, when transmission data (predetermined number of segments) reaches a reception-side apparatus, the reception-side apparatus transmits an acknowledgment (ACK) to notify a transmission source that the data has reached the reception-side apparatus. The same effect can also be expected by delaying this acknowledgment (see, for example, “Mastering TCP/IP, Introduction, Fourth Edition” by Takafumi Takeshita, Yukio Murayama, Toru Arai, Yukio Karita (Feb. 25, 2007) p. 217).